Fig 1.
Study sites situated within Greater London, UK.
Dots highlight the locations of each of the five study rivers, Ravensbourne, Pool, Wandle, Hogsmill and Brent.
Table 1.
Characteristics of restoration among the study rivers, including total river length (km), % urban (total urban land cover for the study river catchment), restoration project with completion year of the project in parenthesis.
Data for this table are from Smith and Chadwick [39].
Fig 2.
Experimental flux chambers: 10 mL sediment from the benthic zone were randomly collected, transferred into separate 50 mL falcon tubes and mixed with 35 mL stream water.
For N samples, 10 mL water (2.5 mL for NH4+ and 7.5 mL for NO3- analysis) was extracted after the sediment had settled (T = 0 minutes), and after both 3 (T = 3 minutes) and 10 minutes (T = 10 minutes). The initial 0–3 minutes flux represented a “physical” disturbance event, while the 3–10 minutes flux reflected a “biogeochemical” flux.
Table 2.
A summary of ranges and averages (N = 20) of stream water NH4+ (μg L-) and NO3- (mg L-1) concentrations in restored and unrestored reaches of London rivers during the spring months of 2016.
Values in parenthesis are one standard error. Significant differences between restored and unrestored reaches are in bold; difference among rivers are indicated by letter groupings.
Fig 3.
Average NH4+ fluxes (μg N m-2 sec-1) among (a) the study rivers (restored and unrestored combined) and between (b) the combined restored and unrestored reaches from all London rivers. Columns represent average values (N = 12–20) + one standard error. Both physical disturbance (T = 0–3 minutes) and biogeochemical activity (T = 3–10 minutes) are presented in each panel. There was no significance different between river NH4+ fluxes over the 0–3 minutes period, nor between restored or unrestored reaches at both 0–3 and 3–10 minutes. Rivers with different letters show significant differences in fluxes over the 3–10 minutes. Positive flux values represent uptake/removal of nutrients from the water column and negative flux values represent release of nutrients from the sediment (regeneration).
Fig 4.
Average NO3- fluxes (μg N m-2 sec-1) among a) the study rivers (restored and unrestored combined) and between (b) the combined restored and unrestored reaches from all London rivers. Columns represent average values (N = 12–20) + one standard error. Both physical disturbance (T = 0–3 minutes) and biogeochemical activity (T = 3–10 minutes) are presented in each panel. There was no significant difference in NO3- fluxes between rivers. However, there was a significant regeneration of NO3- from sediment in unrestored sites over the 0–3 minutes period, but not difference between fluxes at 3–10 minutes. Positive flux values represent uptake/removal of nutrients from the water column and negative flux values represent release of nutrients from the sediment (regeneration).
Table 3.
A summary of N flux averages (μg N m-2 sec-1) of site-specific measurement (N = 12–20).
Values in parenthesis are one standard error. Significant differences between restored and unrestored reaches are in bold. Positive flux values represent uptake/removal of nutrients from the water column and negative flux values represent release of nutrients from the sediment (regeneration). Uptake is shaded brown and regeneration is shade blue. Overall, there were no constant patterns in the magnitude or direction of flux among all measurements.
Table 4.
A summary of the average (N = 12–20) sediment grain size, Chl-a, and percentage total organic matter.
Values in parenthesis are one standard error. Significant differences between restored and unrestored reaches are in bold; difference among rivers are indicated by letter groupings.